Recently, there is known an engine stop and start control apparatus for automatically stopping an internal combustion engine (hereinafter, also referred to as “engine”) when the vehicle stops and for automatically restarting the engine to start the vehicle when an instruction to start is given in the stopped state, in order to reduce a fuel consumption amount and exhaust gas during idling, from the viewpoint of environmental conservation, resources and energy saving or the like. This control is also called “idling stop” or the like.
It is known that, when the idling stop is automatically carried out, it is effective to control the stop position of the engine in order to minimize required energy at the time of starting the engine. Minimizing the required energy at the time of starting the engine brings about the advantages that an engine starting device used after idling stop such as a motor generator (MG) can be miniaturized, and the useful life of a battery can be elongated by reducing the electric energy.
As a method for controlling the stop position of the engine, there are proposed methods for executing fuel cut when a specific cylinder comes to a position of a predetermined crank angle, and for stopping the engine at a predetermined position by setting a predicted value of a compression torque at the time of stopping the engine and by producing a counter torque equivalent to the predicted compression torque to establish a balance.
Also, there is proposed an engine start apparatus in which the starter is rotated in a normal direction after the engine stop, and if the crank angle is at the crank angle stop position at which the starting torque of a starter becomes large, the crankshaft is rotated in a reverse direction to a crank angle stop position at which a starting torque becomes small before the next engine start, thereby improving the starting performance at the time of starting the engine. This method is disclosed in the Japanese Patent Application Laid-Open under No. 2000-283010.
Further, there is known the engine start apparatus for executing the next engine start by combusting the fuel in the cylinder supplied during the expansion stroke at the time of the engine stop. This method is disclosed in the Japanese Patent Application Laid-Open under No. 2002-4985.
However, in the method for executing the fuel cut at the predetermined crank angle for the specific cylinder in order to stop the engine at the predetermined position, since the states of engine loads of auxiliary machines and the like at the time of executing the fuel cut and the number of engine revolution immediately before the fuel cut are not always constant, the falling manner of the number of the engine revolution after executing the fuel cut until actual stopping of the engine may vary. No matter how small it may be, such a variation finally brings about a large accumulated difference. Consequently, it is practically difficult that the engine stop position is always controlled in a constant manner.
In the method for controlling the engine stop position by utilizing the balance with the compression torque at the time of stopping the engine, first, it is difficult to accurately predict the value of the compression torque. This is because the value of the compression torque is affected by an air amount leaking out via a piston ring and is varied by the speed of the vehicle. Further, a large motor is needed because a large torque has to be produced in order to balance with the compression torque, and hence the power consumption becomes large.
In the method for moving the crank angle to the position at which the starting torque becomes small by utilizing the motor after stopping the engine, since a large torque is needed to rotate the crankshaft after stopping the engine, a large motor is needed, after all.
On the other hand, as to the start control of the engine, by controlling the engine stop position, the necessary torque at the time of starting can be small and a motor for the engine start used at the time of idling stop can be miniaturized, as explained above. However, as the motor for starting is miniaturized, the possible output torque becomes small. As a result, there occurs a problem that the time until the completion of the first explosion of the engine becomes long.
Also, when the motor for starting is miniaturized, falling of the torque when the number of engine revolution increases becomes large. This is especially remarkable in a low voltage battery about 12V. Therefore, even if a piston of the cylinder in the compression stroke can get over the first compression stroke top dead center by the motoring by the starter motor, the piston may not get over the next compression stroke top dead center because enough inertia energy of the engine cannot be generated due to the decreasing outputting torque of the starter motor when the number of engine revolution increases. In the worst case, the motor may lock around the top dead center.
Further, there may also occur a problem that the time until the completion of the first explosion becomes long because it takes considerable time to determine the cylinder when the number of engine revolution is low.